A variety of different printing processes for use in printing presses are known. One such printing process is inkjet printing or ink-jet printing. In this process, individual droplets of coating medium are ejected through nozzles of print heads and are transferred to a printing material so as to produce a printed image on the printing material. By actuating a plurality of nozzles individually, different printed images can be produced. Since no fixed printing form is involved, each printed product can be designed individually. This allows personalized printed products to be produced, and/or, since printing forms are dispensed with, allows small print runs of printed products to be produced at low cost.
The precise alignment of printed images on the front and back sides of a printing material that is imprinted on both sides is referred to as register (DIN 16500-2). In multicolor printing, the merging and precise correlation of individual printed images of different colors to form a single image is referred to as color-to-color registration (DIN 16500-2). Suitable measures are also necessary in inkjet printing in order to maintain color-to-color registration and/or register.
If a printing unit has more than one print head, it is important for the settings of the print heads to be aligned with one another, in order to achieve a high-quality print result. For example, the print heads must be aligned correctly with respect to their relative position and must be actuated at the proper time. Methods and/or devices which in some cases may be costly are used for this purpose.
EP 2 202 081 A1, DE 10 2011 076 899 A1 and JP 2003-063707 A each disclose a printing press in which the printing press comprises a first printing unit having at least one inkjet print head.
WO 2013/040455A1 discloses a positioning device which can be used to move a print head in and opposite at least one direction.
EP 0 938 973 A2 discloses a method in which inkjet print heads assigned to different colors of ink are aligned relative to one another in a first process, after which, for each color of ink, a print head involved in the first process is used as a reference print head, which is used for aligning other print heads of the respective ink color in relation to the reference print head.
EP 2 444 850 A2 discloses a method for aligning LED print heads relative to one another.
US 2012/0038697 A1 discloses a method for aligning print heads relative to one another.
US 2010/0182382 A1 discloses a movable sensor, which is used to detect the settings of different print heads relative to one another.
US 2011/0273502 A1 discloses a printing press and a method in which a printed image is detected by means of a sensor embodied as a sensor array. The sensor is either large enough that it does not need to be moved in order to detect the entire printed image, or this one sensor is moved along the printing material.
US 2002/0041299 A1 discloses a method and a device in which the relative positions of print heads are adjusted first in a longitudinal direction and then in a transverse direction. A detection is carried out in each case by row between adjacent print heads.
US 2012/0033006 A1 discloses a method and a printing press, in which a printed image is detected by a line sensor. Print heads assigned to an individual color of ink are aligned with one another, after which alignments of print heads assigned to different colors of ink relative to one another are carried out.